Check if the sleep command returns due to a pending interrupt
in the standby unit. If this happens, try and ack the IRQ
before re-trying the resume.

It is currently unclear whether the resume can be backed out
of at this stage as this could cause a problem with level
based interrupts.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>